Originally Posted by Porschefile
LC wears out the clutches and the gears, using S6 wears out the gears but not the clutches. It just shifts so fast and hard that it puts unnecessary pressure on the gearbox. Try it under acceleration at high rpm and you can feel it. Similar to the fastest shift mode in SMG E46's, a few track guys have busted trans that way.
Basically it shifts up without allowing the revs to drop 100% to match the next gear. So it feels like it "surges" forward when you shift.
Personally I stick with S4 on track, still shifts very fast without bucking at all. S5 I've done before on track but the tiny decrease in shift time isn't worth the increased wear to me.
I drive in S5 all the time - even to the shops with the kids in the back!